Nonlinearity, frequency stability and device-to-device variability in nano-contact spin torque oscillators with grainy thin films
(English)Manuscript (preprint) (Other academic)
In nano-contact spin torque oscillators with a frequency range of 10-65 GHz, the propagating spin wave mode attracts interest due both to its high frequency stability and prospective use in magnonic devices. Its dependence of the frequency on the bias current however displays device-to-device variability on the order of several hundred MHz, with device specific nonlinearities that can be either continuous or discontinuous and have negative impact on the frequency stability. A model for this behavior is however still lacking. By using micromagnetic simulations, we investigate the impact of imperfections in the spin wave-carrying free magnetic layer and find that nonlinearities can be created when the propagating spin wave is reflected back to the active region. The oscillation then self-locks at the frequency of the resonant wavelength, resulting in a standing spin wave pattern. Simulations including nine randomly generated film structures with 30 nm-sized grains and exchange-reduced inter-grain boundaries give qualitative and partially quantitative agreement with experimental measurements. The results point out the spin wave-reflecting grain boundaries as a source of device nonlinearity, manufacturing variability and frequency destabilization.
Spin torque, spin waves, magnetization dynamics, thin films, microstructure, microwaves, phase noise
Other Physics Topics
IdentifiersURN: urn:nbn:se:kth:diva-188544OAI: oai:DiVA.org:kth-188544DiVA: diva2:936364
FunderSwedish Research Council
Qc 201606162016-06-132016-06-132016-06-20Bibliographically approved